1. Field of the Invention
The invention relates to a method of removing nitrogen oxides (NO.sub.x) from flue gases by way of a multi-stage washing process with nitric acid (HNO.sub.3) solution to which hydrogen peroxide (H.sub.2 O.sub.2) is added, with the flue gases previously having been freed of H.sub.2 O.sub.2 -decomposing and/or corrosive contaminants, such as, for example, sulfur dioxide (SO.sub.2), hydrogen chloride (HCl) or hydrogen fluoride (HF) and of solid particles.
2. Background of the Related Art
For the combined removal of sulfur dioxide (SO.sub.2) and nitrogen oxides (NO.sub.x), a multi-stage process is known from Federal Republic of Germany Published Patent Application No. 3,436,699 which, in its first stages, washes out sulfur dioxide with the aid of sulfuric acid (H.sub.2 SO.sub.4) and hydrogen peroxide (H.sub.2 O.sub.2) while in the last stage nitrogen oxides are removed by means of nitric acid (HNO.sub.3) and H.sub.2 O.sub.2. Processes are also known which, for the sole removal of nitrogen oxides, likewise operate with HNO.sub.3 /H.sub.2 O.sub.2 mixtures. With these prior art processes, the degrees of purity required today--for example, NO.sub.x not exceeding 70 mg/Nm3--cannot be realized.